Illumination system

ABSTRACT

An illumination system having four lamps arranged orthogonally around a subject to be illuminated with each lamp positioned outside the corresponding adjacent edge of the subject. A reflector system having a cylindrical surface and a plurality of flat reflectors are associated with each of the lamps for directing light rays to the subject from the adjacent edge thereof to the edge opposite thereto.

United States Patent 1191 [111 3,777,135 Rees Dec. 4, 1973 [54]ILLUMINATION SYSTEM 3,428,397 2/1969 Elmer 355 70 [75] Inventor: James DRees Pimford, NY. 3,498,715 3 1970 Gold 355 70 73 A X C 6 R h t NYFOREIGN PATENTS OR APPLICATIONS erox es 64,022 10 1912 Switzerland355/70 [22 Filed: Jul 11, 1972 605,609 2 1926 France 201,755 3/1939Germany 240 41.1

Appl. No.: 270,750

Related US. Application Data Continuation of Ser. No. 157,754, June 28,1971, abandoned, which is a continuation of Ser. No. 813,201, April 3,1969, abandoned.

US. Cl. 240/4l.35 R, 240/41.1, 240/41.3, 240/103, 355/70 Int. Cl F21v7/00, G03b 27/54 Field of Search 240/4l.1, 41.3, 41.35, 240/103; 355/67,68, 69, 70

References Cited UNITED STATES PATENTS 2/1968 Bentzman 240/41.35

Primary Examiner-Samuel S. Matthews Assistant Examiner-Richard M. SheerAttorney-Hemard A. Chiama [5 7] ABSTRACT An illumination system havingfour lamps arranged orthogonally around a subject to be illuminated witheach lamp positioned outside the corresponding adjacent edge of thesubject. A reflector system having a cylindrical surface and a pluralityof flat reflectors are associated with each of the lamps for directinglight rays to the subject from the adjacent edge thereof to the edgeopposite thereto.

13 Claims, 4 Drawing Figures PATENIED 41973 SIEEI 1 OF 4 INVENTOR. JAMESD. REES JR.

AT TOR NE Y PATENIEI] UEII 41975 SHLEI 2 OF 4 PATENTED DEC 75 sum 3 0F 4PATENTEI] BEE 4 7 SHEET l 0F 4 ILLUMINATION SYSTEM This is acontinuation of application Ser. No. 157,754, filed June 28, 1971,which, in turn, is a continuation of application Ser. No. 813,201, filedApr. 3, 1969, both now abandoned.

This invention relates to illumination systems, and particularly, toimprovements in the arrangement of lamps and associated reflectorsrelative to a subjectto be illuminated. The illumination system arrangedin accordance with the present invention is particularly adapted for usewith optical systems for illuminating originals to be reproduced inautomatic copiers/duplicators that are adapted for high speed operationand capable of having its sequence timing varied thereby permittingvariable speeds of output.

As is well known in recent years, the steadily increasing size ofvarious industries has required an enormous increase in the amount ofpaper work that must be accomplished, maintained, and made available forwide interplant or department circulation. In the present day commercialautomatic copier/reproduction machines, which are adapted to producecopies of between 5 and 60 8 X l 1 inch sheets of copy per minute, thephotoreceptor device is in the form of a drum which rotates in timedunison relative to a plurality of processing stations. The limitingfeature in these present day machines is the use of the xerographic drumwhich seriously limits the positioning and action of each of theprocessing devices and, in particular, the requirement of presenting aflowingimage upon the xerograph ic drum as a document is being scanned.

The mechanism which accomplishes the scan of a fixed document in thedrum type copier/duplicator generally involves a slidable carriage forsupporting illumination lamps in addition to drive mechanisms, levers,pulleys, switches, etc. for accomplishing scanning of the document. Asthe demands for faster copying or duplicating has come about, theseconventional machines generally have been modified in their respectivedrive systems and'electrical circuits in order to accomplish a fasterscan for the scanning mechanisms already in the machine. The result ofthese modifications is to propel the structures that go to make up thescanning mechanisms at very great speeds and, as will be apparent, willplace undue burden upon the structural supports of the machine and thescanning mechanism.

As a solution for overcoming the multitude of disadvantages for highspeed copying, the latest machine concept for copiers utilizes flashexposure of a document and the arrangement of a moving photoconductormaterial in a flat condition at the instant of exposure. However, inorder to overcome the loss of exposure time that these copiers usuallydemand the intensity of the illumination lamps, in order to accomplishadequate imaging, must be extremely high requiring specially designedlamps and overly large power sources.

It is therefore the principal object of this invention to improveillumination systems for effecting maximum capability of the lampsutilized therein, which system is capable for general copyingapplications and for making high speed copies in variable timesequences.

Another object of this invention is to improve illumination systems forflat objects wherein dark spots and light spots are substantiallyeliminated.

Another object of this invention is to improve illumination systemswhereby light rays produced thereby when directed upon an object beingilluminated is such as to effect homogeneous illumination at an imageplane.

Another object of this invention is to improve illumination systemsemploying elongated lamps by arranging the same so as to achieve uniformillumination at maximum intensity and with a minimum of powerrequirements.

These and'other objects of this invention are obtained by means of theorthogonal arrangement of a plurality of elongated light sources orlamps which are positioned outside the outer edges of a flat objectbeing illuminated. The light rays from each of the lamps are directed onthe adjacent edge of the object and extend acrossthe object to theremote edge thereof thereby overlapping the light rays from the otherlamps. In conjunction with each lamp there is provided a semicylindricalreflector and planar reflectors arranged edge to edge at differentangles relative to each other and in position adjacent one edge of thesemicylindrical reflector for directing different light rays therefromfor optimizing the projection of the light rays from each lamp to theobject.

For a better understanding of the invention as Well as other objects andfurther features thereof, reference is had to the following detaileddescription of the invention to be read in conjunction with theaccompanying drawings, wherein:

FIG. 1 is a schematic sectional view of a typical reproduction machineshowing the various electrostatic processing stations;

FIG. 2 is an isometric schematic view of a portion of the lamp assemblyof an illumination system arranged in accordance with the presentinvention;

FIG. 3 is a partial top view of a portionof the lamp assembly anddocument platen; and

FIG. 4 is a sectional view of one side of the lamp assembly.

For a general understanding of the illustrated copier/reproductionmachine, in which the invention may be incorporated, reference is had toFIG. 1 in which the various system components for the machine areschematically illustrated. As in all electrostatic systems such as axerographic machine of the type illustrated, a light image of'a documentto be reproduced is projected onto the sensitized surface of axerographic plate to form an electrostatic latent image thereon.Thereafter, the latent image is developed to form xerographic powderimage, corresponding to the latent image on the plate surface. Thepowder image is then electrostatically transferred to a support surfaceto which it may be fused'by a fushing device whereby the powder image iscaused permanently to adhere to the support surface.

In the illustrated machine, an original D to be copied is placed upon atransparent support platen P fixedly arranged in an illumination lampassembly 10 arranged at the left end of the machine as viewed in FIG. 1.While upon the platen, an illumination system, to be described herein,flashes light rays upon the original thereby producing image rayscorresponding to the informational areas on the original. The imagerays, indicated by lines 11 are projected by means of an optical systemfor exposing the photosensitive surface of a xerographic plate at theexposure station A, the plate being in the form of a flexiblephotoconductive belt 12 arranged on a belt assembly generally indicatedby the reference numeral 13.

The photoconductive belt assembly 13 is slidably mounted upon a supportbracket secured to the frame of the machine and is adapted to drive theselenium belt 12 in the direction of the arrow as shown in FIG. 1 at aconstant rate. During this movement of the belt, the light imagingraysof an original are flashed upon the xerographic surface of thebelt. Thebelt surface that intercepts the light rays comprises a layer ofphotoconductive material such as selenium on a conductive backing thatis sensitized prior to exposure by means of a suitable charging coronagenerator device.

The flash exposure of the belt surface to thelight image discharges thephotoconductive layer in the areas struck by light, whereby thereremains on the belt a latent electrostatic image in image configurationcorresponding to the light image projected from the original on thesupporting platen. As the belt surface continues its movement, theelectrostatic image passes through a developing station B in which thereis positioned a developer assembly generally indicated by the referencenumeral l4 and where thebelt is maintained in a flat condition. Thedeveloper assembly 14 comprises a vertical conveying mechanism whichcarries developing material to the upper part of the belt assembly l3whereat the material is dispensed'and directed to cascade down over theupwardly moving inclined selenium belt 12 in order to providedevelopment of the electrostatic image. As the developing material iscascaded over the xerographic plate, toner particles in the developmentmaterial are deposited on the belt surface to form powder images.

The developed electrostatic image is transported by the belt to atransfer station C whereat a sheet of copy paper is moved at a speedapproximately in synchronism with the moving belt in order to accomplishtransfer of the developed image. There is provided at this station asheet transport mechanism generally indicated at 16 adapted to transportsheets of paper from a paper handling mechanism generally indicated bythe reference numberal 18 to the developed powder image on the belt atthe station C. The transfer of the developed image from the seleniumbelt surface to sheet material is effected by means of'a suitable coronatransfer device that is located within the sheet transport mechanism tothe point of contact between the sheet and selenium belt as the sheetpasses the transfer station C.

After the sheet is stripped from the belt 12 it is conveyed into a fuserassembly generally indicated by the reference numeral 20 wherein thedeveloped and transferred xerographic powder image on the sheet materialis permanently affixed thereto. After fusing the finished copy isdischarged from the apparatus at a suitable point for collectionexternally of the apparatus.

Suitable drive means may be arranged to drive the selenium belt 12 inconjunction with timed flash exposure of an original to be copied toeffect conveying and cascade of toner material, to separate and feedsheets of paper and to transport the same across the transfer station Cand to convey the sheet of paper through the fuser assembly in timedsequence to produce copies of the original.

It is believed that the foregoing description is sufficient for thepurposes of this application to show the general operation of anelectrostatic copier using an illumina-tion system constructed inaccordance with the invention. For further details concerning thespecific construction of the electrostatic copier, reference is made toU.S. Pat. No. 3,661,452, issued May 9, 1972 in the name of Hewes et al.

The illumination system of the present invention is illustrated indetail in FIGS. 2-4 and is designed for irradiating the diffuselyreflecting original D such that the image of the original produced by alens has irradiance uniformity to a maximum of :5 percent. This uniformimage irradiance is obtained by the use of four linear light sources L IL and L and their associated reflectors R R R and R arrangedorthogonally relative to the original. The arrangement is such as tocompensate for the relative illumination functions of the lens, forexample, the illumination falloff due to vignetting of the opticalaperture for the system and to the cosine to the fourth power law.

Each of the four linear light sources, which may be in the form of axenon flash lamp or other gaseous discharge tube having a smalldiameter, is provided with a semi-cylindrical reflector and at least oneplano reflector. The radio-metric equations for the reflectors areutilized to project reflected light from aplaten supporting an originalonto an image plane where the irradiated image has nearly uniformirradiance.

As shown in FIGS. 2 and 3, the lamps L,, L L and L, are arranged alongthe sides of a rectangle somewhat larger than the rectangle defined bythe original D. The inner edges of the reflectors R R R and R beingparallel to the respective lamps are also arranged as the sides of arectangle having its inner edges spaced slightly outwardly from theedges which define the original. With this arrangement, the light rayswhich emanate from each of the lamps, are directed toward the original,to impinge thereon at various angles other than directly or at Thisarrangement, then, eliminates direct perpendicular impingement of thelight rays upon the document thereby preventing excessively highintensity illumination of the edges of the documentifsuch were extendedover the light sources.

In order to provide homogeneous illumination wherein there will be aminimum amount of variation in the image irradiance from an originaland, to increase the amount of light that can be directed toward theoriginal D to near perfect efficiency, the illumination system isprovided with a semi-cylindrical shape reflective surface in combinationwith 'at least one plano reflective'surface for each of the linearlamps. These-reflective surfaces are designed to direct light upon theoriginal being illuminated and are so arranged that the impinging raysof one lamp and its corresponding reflective surfaces overlap with theimpinging rays of the opposing lamp and its corresponding reflectivesurfaces. These reflected rays coupled with the rays emanating, directlyfrom each of the lamps upon the original and result in a more uniform,homogeneous illumination of the photoconductive'surface.

Each of the reflectors, and for simplicity the reflector R will be theonly one described in detail, comprises a first reflector surface Rhaving the form of a right circular cylinder with the axis of thesurface of revolution parallel to and offset relative the axis of thelinear lamp L by an amount approximately equal to the radius of thelamp. The reflector surfaces R one for each of the reflectors in theillumination system, define the inner limits of the four assembledreflectors. When assembled, the surfaces define an opening through whichthe light rays emanating from an illuminated Original are directedtherethrough to a projection lens for the document illumination system.Light rays, as illustrated in FIG. 4 by lines A, and A, emanate from thelamp L, and from the cone A, of light directly in back of the lamp andreflected by the surface R through the lamp. The lines A, and A extendto the adjacent and furthermost edges, respectively, of the document Dand define the outer limits of the light reaching the document from lampL, and cone A,,. In addition, withthe axis of the lamp L, being locatedadjacent the axis of the cylindrical surface R light is also reflectedfrom this surface and directed upon the original.

Joined along the outer edge of the reflector surface R,, is a secondreflector surface R, in the form of an elongated plane surface havingits inner longitudinal edge connected to the edge of the surface R, andarranged to redirect some of the light rays from the lamp L, between thelines B, and B, that extend to the adjacent and furthermost edges,respectively of the document. The light falling upon the surface R, thatis redirected upon the document would otherwise be lost for illuminationpurposes if this surface was not provided. The ray 8, may be made tofall very near to the ray A, in order to minimize the light that may belost at the juncture of the surfaces R, and R,,. The line B, and itsoriginating direct light line that extends between the lamp and thesurface has been illustrated relative to a point away from the R -Rjunction point for clarity reasons. The only light that is lost byoperation of the surfaces R R would be at this junction and then onlyfor a very narrow cone of light rays, too small to be i1- lustrated.

In order to enhance the illumination uniformity by the illuminationsystem at the image plane, which for the machine of FIG. 1 is the sameas the exposure station A, a second elongated plano reflective surface Ris provided and has one of its longitudinal edges joined to the outerlongitudinal edge of the plano surface R,,. The surface R redirectsstill more of the light emanating from the lamp L, that would beotherwise lost, along light rays extending away from the document andthe other surfaces R,,, R,,. The plane of the surface R is at an anglerelative to the plane of the surface R, such that the light rays fallingthereon from the .lamp L, and

from the cone C, immediately behind the lamp from the surface RC isreflected and directed along the light lines C, and C These lines definethe limits of the light reaching the documentfrom the surface RC. As wasthe case for the R,,R,, junction, the light line C, is illustrated inFIG. 4 slightly away from .the R,,R junction in order to permit bettervisualization. In actual practice, the line C would be effectivelycloser to the R -R junction thereby minimizing light losses due to thisreflector jun n.

Additional efleciency is possible with the illumination system by theprovision of a third elongated plano reflective surface R, having itsinner longitudinal edge connected to the outer edge of the surface R andat an angle relative thereto for redirecting additional light from thelamp L, upon the document. The surface R is arranged so as to redirectlight reaching the same from the lamp and from the cone D, immediatelybehind the lamp from the surface R upon the document between light linesD, and D These lines define the limits of the light reaching thedocument from the reflective surface R As in the previous cases, theline D, has been shown slightly displaced relative to-the R,.R,,junction in order to permit better illustration thereof.

The angles between the planes of the surfaces R,,, R, and R, are lessthan degrees relative to one another.

In actual practice, there is negligible light losses from the linearjunction R,,-R,,, R,,-R R -R of the reflective surfaces. The cones A B Cand D having been drawn in FIG. 4 to correspond with their respectivelight lines reaching the document being illuminated. As shown, there areappreciable gaps between the cones signifying light losses in the gaps.Actually, with light lines impinging upon points closer to the abovereferred to junctions, the cone angles would be larger and the gapstherebetween smaller and negligible. The dimension for the width of eachof the surfaces R,,, R, and R, is chosen so that the portions of thesurfaces nearest the edges will effect reflection to the edges of thedocument,no more, no less. In this manner, there is a minimum of loss oflight directed upon the reflecting surfaces.

From an analysis of FIG. 2, in conjunction with the description above,it will be seen that each lamp L,, L,, L,, and L, generates sevenimages, some real and some virtual, which serves as light sources.Again, using lamp L, as typical of the operation of the other lamps inthe illumination system, the seven images are disposed approximately inthe portions illustrated in FIG. 2. With the lamp L, being slightlydisplaced relative to the 1ongitudinal axis .of the cylindricalreflector R,,, the first read image thereof is illustrated at L, beingproduced by the internal reflection of the reflective surface R,,. Boththe lamp L, and its image L,, serving as light sources for the reflectorR in turn generate the virtual images L, and L, respectively. Byreflecting from the reflective surface R the lamp L, and its imageL,also effect the virtual images at L, and L,". Similarly, thereflective surface, R, will effect the virtual images L, and L, from thelamp L, and its image L,, respectively. Each of the seven images willserve as light sources for illuminating the document D, therebyoptimizing the efficiency of the illumination system.

From the foregoing it will be apparent that the reflecting surfaces R,,,R,, R, and R, serve to reflect the light rays emanating from the lamp L,upon the original D between both extreme edges thereof in overlappingfashion. This means the light reflected from the surface R, will bedirected upon the document starting from line ray A, coincident with theadjacent edges of the original, and sweeping across the document to theother edge thereof terminating in the line ray A Light reflected fromthe plano reflectors R,,, R, and R, are directed upon the documentbetween the line rays B,, B C,, C,,; and D,, D, respectively.

Similarly, as viewed in FIGS. 2 and 3, the reflector R, serves toreflect light from the lamp L upon the original D. The light rays soreflected overlap those reflected from the reflecting surfaces of thereflector R,. In similar fashion, light is directed from the reflectorsR and R, by reflection from the lamps L,, and L, respectively, upon theoriginal in overlapping ray-trace arrangement.

The effect then, of the use of four orthogonally arranged lamps arrangedbeyond the edges of an original being illuminated, and especially withthe provision of the reflecting. surfaces for each of the lamps and therelative positions thereof, an original is illuminated in such a mannerthat the object irradiance is cos. or otherwise circularly symetricalfor the center point of the surface of the original. It will be apparentfrom this arrangement of reflecting surfaces that the illuminationassembly makes effective use of a large part of the light flux emittedfrom the light sources except for those areas wherein reflection lossesare behind the lamps themselves. It will be appreciated from theforegoing that the arrangement of the lamps provides cos. illumination.By incorporating the illustrated plano reflectors R R and R with each ofthe lamps, the resultant illumination profile for an object beingilluminated is changed to be symmetrical. It will also be appreciatedthat the optimum illumination is available for an arrangement of lightsources and reflectors which, in themselves, are of simple design,involving little manufacturing skill and expense and may be the resultof relatively calculations. Each of the reflectors are made up of onecylindrical surface and one or more plane surfaces rather than somecomplex surfaces, such as ellipses, spirals, or combinations.

Each of the lamps L L L and L is connected to a suitable sourceelectrical circuit for energizing these lamps. For the particularreproduction machine illustrated in FIG. 2, the particular electricalcircuit for energizing the lamps should be in the 'form of a flashingcircuit which will energize the lamps for short periods of time, suchas, for example, 100 microseconds. In this particular use, this shortperiod of time will be suitable for flash exposing the original D upon aphotoreceptor surface such, for example, as the selenium belt 12.

The image forming light rays emanating from the original D duringillumination thereof are directed to a suitable projection lens system30. Details of the lens system and mirrors 32 therefor and the housingsfor containing and supporting the illumination system as well as thelens system are not necessary for understanding the present invention.Further details of such matters may be derived from the US. Pat.application Ser. No. 731,960, filed May 24, 1968 in the name ofStarkweather et al., the application being assigned to same assignee asthe present application.

The illumination system is adapted to present light image representationof an original document upon the selenium belt 12 sequentially intimedrelation to the movement of the belt which in the particularxerographic reproduction apparatus illustrated, continuously movesduring the xerographic processing stations. The light image of theoriginal being reproduced, is directed out of a housing for theillumination system and through a suitable rectangular opening on theside of the machine adjacent the selenium belt 12. The housing may serveas a light shield for the selenium belt in order to present extraneouslight from impinging upon a belt during use of the apparatus.

While the invention has been described with reference to the structuresdisclosed herein, it is not to be confined to the details set forth andthis application is intended to cover such modifications or changes asmay come within the purpose of the improvements of the following claims.

What is claimed is:

1. An illumination system for illuminating a planar object defined by aplurality of boundaries including a plurality of illumination devices,one being arranged generally in parallel with one of at least twoopposing boundaries of the object, and another of the devices beingarranged generally in parallel with the other of the opposingboundaries,

each of said devices having an elongated light source and a reflectingsurface of concave configuration disposed parallel to and adjacent therespective light source to reflect light rays from its respective lightsource and directly project the rays upon the object,

each of said devices having a reflecting surface of planar configurationfor its respective light source and disposed parallel to and adjacentsaid light source to recieve some of the light rays emanating directlyfrom its respective light source and to direct these rays upon theobject,

each of said illumination devices having its light source and reflectingsurfaces disposed relative to one another for directing light raysrespectively from one of the opposing boundaries to the other with anintensity that varies decreasingly from the former to the latter.

2. An illumination system for illuminating a planar object defined by aplurality of boundaries including a plurality of illumination devices,one being arranged generally in parallel with one of at least twoopposing boundaries of the object, and another of the devices beingarranged generally in parallel with the other of the opposingboundaries,

each of said devices having an elongated light source and reflectingsurface of concave configuration disposed parallel to and adjacent therespective light source to reflect light rays from its respective lightsource and directly project the rays upon the object,

each of said devices having a reflecting surface of planar configurationfor its respective light source and disposed parallel to and adjacentsaid light source to receive some of the light rays emanating directlyfrom its respective light source and to direct these rays upon theobject,

each of the illumination devices having its light source and reflectingsurfaces disposed relative to one another for directing light raysrespectively from one of the opposing boundaries to the other with anintensity that varies decreasingly from the former to the latter,.saidvariation in intensity from one of the devices being substantially equalto the .variation in intensity of another of the devices.

3. The illumination system of claim 1 for planar objects having arectangular shape and the illumination system comprising four lightsources, one parallel to each of the boundaries of the object, and saidreflecting surfaces for each of the light sources.

4. The illumination system of claim 1 wherein each light source and itsassociated concave reflecting surface are positioned outside of thecorresponding boundary of the object.

5. The illumination system of claim 2 wherein each of said deviceshaving a second reflecting surface of planar configuration disposedparallel to and adjacent 7. The illumination system in claim whereinsaid planar reflecting surfaces are at angles less than 180 relative toone another. a

8. In a utilization device wherein an object is arranged to beilluminated from one boundary to another boundary thereof, anillumination device comprising an elongated light source disposed toproject light rays directly upon the object, an element havingreflective surface of concave configuration disposed parallel to andadjacent the light source for receiving light rays therefrom andreflecting the same directly upon the object, an element having areflecting surface of planar configuration extending along said concavesurface and disposed parallel to and adjacent said light source toreceive some of the light rays directly from said source and to reflectthe same directly upon the object, said light source and reflectingsurfaces disposed for directing light rays respectively from said oneboundary of the object to said another boundary with an intensity thatvaries decreasingly from the former to the latter.

9. In a utilization device wherein an object is arranged to beilluminated from one boundary to another thereof, an illumination devicecomprising an elongated light source disposed to project light raysdirectly upon the object, an element having a reflective surface ofconcave configuration disposed parallel to and adjacent the light sourcefor receiving light rays therefrom and reflecting the same directly uponthe object, an element having a plurality of reflecting surfaces ofplanar configuration extending along with said concave surface with eachplanar surface disposed parallel to and adjacent said light source toreceive some of the light rays directly from said source and to reflectthe same directly upon the object in superimposed relation to the otherrays directed to the object, said light source and reflecting surfacesdisposed for directing light rays respectively from said boundary of theobject to said another boundary with an intensity that variesdecreasingly from the former to the latter.

10. In a projection apparatus for illuminating a planar object having atleast two opposed sides and directing light rays emanating therefromthrough a lens system and onto an image plane, the combination includinga plurality of illumination devices, one being disposed adjacent one ofthe sides of the object and another device disposed adjacent the otherside, each of the devices having an elongated light source arrangedgenerally parallel to the respective sides of the object, each of saidlight sources projecting light rays therefrom directly upon the object,each of said devices having an element formed with a reflecting surfaceof right cylindrical configuration disposed parallel to and adjacenteach of said light sources and reflecting light rays reaching said firstsurface from said source and directing the same upon the object insuperimposed relation to the rays reaching the object directly from saidsource, said element having a reflecting surface of planar configurationextending along each cylindrical surface to receive some of the lightrays directly from each source and to reflect the same directly upon theobject,

each of said devices having its light source and reflecting surfacesdisposed relative to one another for directing light rays respectivelyfrom one of the opposed sides to the other with an intensity that variesdecreasingly from the former to the latter.

11. In a projection apparatus for illuminating a planar object having atleast two opposed sides and directing light rays emanating therefromthrough a lens system and onto an image plane, the combination includinga plurality of illumination devices, one being disposed adjacent one ofthe sides of the object and another device disposed adjacent the otherside, each of the devices having an elongated light source armgedgenerally parallel to the respective Sides of the object, each of saidlight sources projecting light rays therefrom directly upon the object,

each of said devices having an element formed with a reflecting surfaceof right cylindrical configuration disposed parallel to and adjacenteach of said light sources and reflecting light rays reaching said firstsurface from said source and directing the same upon the object insuperimposed relation to the rays reaching the object directly from saidsource,

said element having a reflecting surface of planar configurationextending along each cylindrical surface to receive some of the lightrays directly from each source and to reflect the same directly upon theobject,

each of said devices having its light source and reflecting surfacesdisposed relative to one another for directing light rays respectivelyfrom one of the opposed sides to the other with an intensity that variesdecreasingly from the former to the latter, said variation in intensityfrom one of the devices being substantially equal to the variation inintensity of another of the devices.

12. In a utilization device wherein a planar object is arranged to beilluminated and the light rays therefrom projected onto an image plane,an illumination system comprising at least two opposed elongatedillumination devices each having a light source and reflecting meansarranged along the object such that each of at least two oppositeboundaries of the object has one of said illuminating devices adjacentthereto, each of said light sources having its longitudinal axisdisposed outside the boundary of the object adjacent thereto andarranged to directlight rays from that light source directly upon theobject, across the same and to an opposite boundary thereof at anglesless than relative to the plane of the object and with an intensity thatvaries decreasingly from said adjacent boundary to said oppositeboundary, each of said reflecting means including a reflecting surfaceof planar configuration, each of said reflecting means together with itsassociated planar reflecting surface being arranged relative to itscorresponding light source for reflecting light rays from that sourceand to direct these rays between said adjacent boundary and saidopposite boundary with an intensity that varies decreasingly from theformer to the latter, said variations in intensities from each ofsaid'illumination devices being substantially equal whereby theresultant illumination irradiance at the image plane is substantiallyhomogeneous.

13. In a utilization device wherein a planar object is arranged to beilluminated and the light rays therefrom projected onto an image plane,an illumination system comprising at least two opposed elongatedillumination devices each having a light source and a reflecting neous.

1 2 boundary to said opposite boundary, said variation in intensity ofone of said illumination devices being substantially equal and from anopposite directional orientation relative to the variation of intensityof the other illumination device whereby the resultant irradianceillumination at the image plane is substantially homoge-

1. An illumination system for illuminating a planar object defined by aplurality of boundaries including a plurality of illumination devices,one being arranged generally in parallel with one of at least twoopposing boundaries of the object, and another of the devices beingarranged generally in parallel with the other of the opposingboundaries, each of said devices having an elongated light source and areflecting surface of concave configuration disposed parallel to andadjacent the respective light source to reflect light rays from itsrespective light source and directly project the rays upon the object,each of said devices having a reflecting surface of planar configurationfor its respective light source and disposed parallel to and adjacentsaid light source to recieve some of the light rays emanating directlyfrom its respective light source and to direct these rays upon theobject, each of said illumination devices having its light source andreflecting surfaces disposed relative to one another for directing lightrays respectively from one of the opposing boundaries to the other withan intensity that varies decreasingly from the former to the latter. 2.An illumination system for illuminating a planar object defined by aplurality of boundaries including a plurality of illumination devices,one being arranged generally in parallel with one of at least twoopposing boundaries of the object, and another of the devices beingarranged generally in parallel with the other of the opposingboundaries, each of said devices having an elongated light source andreflecting surface of concave configuration disposed parallel to andadjacent the respective light source to reflect light rays from itsrespective light source and directly project the rays upon the object,each of said devices having a reflecting surface of planar configurationfor its respective light source and disposed parallel to and adjacentsaid light source to receive some of the light rays emanating directlyfrom its respective light source and to direct these rays upon theobject, each of the illumination devices having its light source andreflecting surfaces disposed relative to one another for directing lightrays respectively from one of the opposing boundaries to the other withan intensity that varies decreasingly from the former to the latter,said variation in intensity from one of the devices being substantiallyequal to the variation in intensity of another of the devices.
 3. Theillumination system of claim 1 for planar objects having a rectangularshape and the illumination system comprising four light sources, oneparallel to each of the boundaries of the object, and said reflectingsurfaces for each of the light sources.
 4. The illumination system ofclaim 1 wherein each light source and its associated concave reflectingsurface are positioned outside of the corresponding boundary of theobject.
 5. The illumination system of claim 2 wherein each of saiddevices having a second reflecting surface of planar configurationdisposed parallel to and adjacent each of said light sources to recivesome of the light rays from its respective light source and to directthese rays upon the object.
 6. The illumination system of claim 5wherein each of said devices having a third reflecting surface of planarconfiguration disposed parallel to and adjacent each of said lightsources to receive still other light rays from its respective lightsource and to direct these rays upon the object.
 7. The illuminationsystem in claim 5 wherein said planar reflecting surfaces are at anglesless than 180* relative to one another.
 8. In a utilization devicewherein an object is arranged to be illuminated from one boundary toanother boundary thereof, an illumination device comprising an elongatedlight source disposed to project light rays directly upon the object, anelement having reflective surface of concave configuration disposedparallel to and adjacent the light source for receiving light raystherefrom and reflecting the same directly upon the object, an elementhaving a reflecting surface of planar configuration extending along saidconcave surface and disposed parallel to and adjacent said light sourceto receive some of the light rays directly from said source and toreflect the same directly upon the object, said light source andreflecting surfaces disposed for directing light rays respectively fromsaid one boundary of the object to said another boundary with anintensity that varies decreasingly from the former to the latter.
 9. Ina utilization device wherein an object is arranged to be illuminatedfrom one boundary to another thereof, an illumination device comprisingan elongated light source disposed to project light rays directly uponthe object, an element having a reflective surface of concaveconfiguration disposed parallel to and adjacent the light source forreceiving light rays therefrom and reflecting the same directly upon theobject, an element having a plurality of reflecting surfaces of planarconfiguration extending along with said concave surface with each planarsurface disposed parallel to and adjacent said light source to receivesome of the light rays directly from said source and to reflect thE samedirectly upon the object in superimposed relation to the other raysdirected to the object, said light source and reflecting surfacesdisposed for directing light rays respectively from said boundary of theobject to said another boundary with an intensity that variesdecreasingly from the former to the latter.
 10. In a projectionapparatus for illuminating a planar object having at least two opposedsides and directing light rays emanating therefrom through a lens systemand onto an image plane, the combination including a plurality ofillumination devices, one being disposed adjacent one of the sides ofthe object and another device disposed adjacent the other side, each ofthe devices having an elongated light source arranged generally parallelto the respective sides of the object, each of said light sourcesprojecting light rays therefrom directly upon the object, each of saiddevices having an element formed with a reflecting surface of rightcylindrical configuration disposed parallel to and adjacent each of saidlight sources and reflecting light rays reaching said first surface fromsaid source and directing the same upon the object in superimposedrelation to the rays reaching the object directly from said source, saidelement having a reflecting surface of planar configuration extendingalong each cylindrical surface to receive some of the light raysdirectly from each source and to reflect the same directly upon theobject, each of said devices having its light source and reflectingsurfaces disposed relative to one another for directing light raysrespectively from one of the opposed sides to the other with anintensity that varies decreasingly from the former to the latter.
 11. Ina projection apparatus for illuminating a planar object having at leasttwo opposed sides and directing light rays emanating therefrom through alens system and onto an image plane, the combination including aplurality of illumination devices, one being disposed adjacent one ofthe sides of the object and another device disposed adjacent the otherside, each of the devices having an elongated light source arrngedgenerally parallel to the respective sides of the object, each of saidlight sources projecting light rays therefrom directly upon the object,each of said devices having an element formed with a reflecting surfaceof right cylindrical configuration disposed parallel to and adjacenteach of said light sources and reflecting light rays reaching said firstsurface from said source and directing the same upon the object insuperimposed relation to the rays reaching the object directly from saidsource, said element having a reflecting surface of planar configurationextending along each cylindrical surface to receive some of the lightrays directly from each source and to reflect the same directly upon theobject, each of said devices having its light source and reflectingsurfaces disposed relative to one another for directing light raysrespectively from one of the opposed sides to the other with anintensity that varies decreasingly from the former to the latter, saidvariation in intensity from one of the devices being substantially equalto the variation in intensity of another of the devices.
 12. In autilization device wherein a planar object is arranged to be illuminatedand the light rays therefrom projected onto an image plane, anillumination system comprising at least two opposed elongatedillumination devices each having a light source and reflecting meansarranged along the object such that each of at least two oppositeboundaries of the object has one of said illuminating devices adjacentthereto, each of said light sources having its longitudinal axisdisposed outside the boundary of the object adjacent thereto andarranged to direct light rays from that light source directly upon theobject, across the same and to an opposite boundary thereof at anglesless than 90* relative to the plane of the Object and with an intensitythat varies decreasingly from said adjacent boundary to said oppositeboundary, each of said reflecting means including a reflecting surfaceof planar configuration, each of said reflecting means together with itsassociated planar reflecting surface being arranged relative to itscorresponding light source for reflecting light rays from that sourceand to direct these rays between said adjacent boundary and saidopposite boundary with an intensity that varies decreasingly from theformer to the latter, said variations in intensities from each of saidillumination devices being substantially equal whereby the resultantillumination irradiance at the image plane is substantially homogeneous.13. In a utilization device wherein a planar object is arranged to beilluminated and the light rays therefrom projected onto an image plane,an illumination system comprising at least two opposed elongatedillumination devices each having a light source and a reflecting meansarranged along the object such that each of at least two oppositeboundaries of the object has one of said illumination devices adjacentthereto, each of said reflecting means including a reflecting surface ofplanar configuration, each of said illumination devices having itslongitudinal axis disposed outside the boundary of the object adjacentthereto and arranged for producing light rays which project upon theobject with an intensity that varies decreasingly from said adjacentboundary to said opposite boundary, said variation in intensity of oneof said illumination devices being substantially equal and from anopposite directional orientation relative to the variation of intensityof the other illumination device whereby the resultant irradianceillumination at the image plane is substantially homogeneous.